Several publications and patents are cited in this application in order to more fully describe the state of the art to which this invention pertains. The disclosure of each of these citations is incorporated by reference herein.
Adenocarcinoma of pancreatic ducts is the fifth leading cause of cancer-related deaths in the United States (1;2). The survival time for patients diagnosed with pancreatic cancer ranges from three to six months on average, with a 5% chance of five-year survival. The highest cure rate occurs if the tumor is truly localized to the pancreas; however, this stage of disease accounts for fewer than 20% of cases. For those patients with localized disease and small cancers (<2 centimeters), with no lymph node metastases and no extension beyond the “capsule” of the pancreas, complete surgical resection can yield actuarial 5-year survival rates of 18% to 24% (3;4). Unfortunately, the signs of early stage pancreatic cancer are vague, and often attributed to other problems by both patients and physicians. More specific symptoms tend to develop after the tumor has grown to invade other organs or blocked the bile ducts. Patients are usually diagnosed at an advanced stage, with a high incidence of associated metastases, which spread throughout the body.
There are no tumor-specific markers for pancreatic cancer; markers such as serum CA19-9 have low specificity (5). 65% of patients with pancreatic cancer will have CA19-9 levels greater than 120 U/L, whereas only 2% of cases of pancreatitis will have levels this high. Indeed, CA-19-9 levels increase with pancreatic cancer (97%) to values greater than 1000 U/L, however most of these cancers will be unresectable. Anti-CA19-9 recognizes a mucin-type glycoprotein sialosyl lewis antigen (6). For over two decades, oligosaccharide structure antigens such as CA19-9, DUPAN2, or CA125 were heavily investigated for the development of serum-based immunoassays for the early detection of cancers. These saccharidic epitopes are carried by high molecular weight glycoproteins called mucins. CA19-9 (7;8) and DUPAN2 (7;9) are present in MUC1 and CA125 is present in MUC16 (10; 11).
Interestingly, both mucin gene expression and the glycosylation pattern of mucins are dysregulated in cancer development and progression. Indeed, a specific mucin expression pattern is usually associated with one type of adenocarcinoma, which is distinct from its normal counterpart. For instance, it has previously been reported that overexpression of the MUC1 gene and aberrant expression of the MUC4 gene is associated with pancreatic cancer development and progression. MUC4 is highly expressed in human pancreatic tumors and pancreatic tumor cell lines, but is minimally or not expressed in normal pancreas or chronic pancreatitis (12–15). MUC4 is expressed by metasplastic ducts and its expression increases with higher grade in Pancreatic intraepithelial neoplasias (PanINs) (16). However, MUC4 is expressed by only 70 to 75% of the pancreatic tumors studied.
Mucins, the main components of the mucus network, are high molecular weight O-glycoproteins expressed and secreted by epithelial cells and in some case by endothelial cells. Their principal function is to protect and lubricate epithelial surfaces, and recent reports demonstrate that mucins and more specifically membrane-bound mucins might play a key role in the initiation and transduction of signals, which trigger apoptosis and/or proliferation. The rMuc4 (rat homologue of human MUC4) forms a ligand-receptor type intramembrane complex with HER2, induces its phosphorylation and triggers survival of cells by repression of apoptosis (17).
Currently, nineteen genes are within the MUC gene family and include: MUC1–2, MUC3, MUC4, MUC5AC, MUC5B, MUC6–13, MUC15–19 (18–22). These mucins can further be grouped in two subfamilies, e.g. secreted mucins and membrane-bound mucins. Secreted mucins are expressed exclusively by specialized epithelial cells, are secreted in the mucus, and demonstrate a restricted expression pattern within the human body. Membrane-bound mucins, composed of MUC1, MUC3, MUC4, MUC12–13, MUC16, and MUC17 often possess EGF-like domains (MUC3, 4, 12, 13, and 17) and appear to share numerous common properties. As compared to the secreted mucins, membrane-bound mucins demonstrate a wide and complex expression pattern. They can be expressed in four distinct forms; 1) membrane-anchored, 2) soluble (proteolytic cleavage of the membrane-bound form), 3) secreted (alternative splice variants), and 4) lacking the tandem repeat array (alternatively spliced variants) (14;23–26). The ratio of one form to another appears to be tissue specific as is association with the physiologic condition, e.g.,(normal or malignant phenotypes) (26;27).